Method of forming valve tappets



Marh1,1932., EWETHERALD A1,848,083

METHOD OF FORMING VALVE TAPPETS Filed Aug. 7, 1929 W, A www,

Patented Mar. 1, 1932 UNrriaD STATES .PATENT OFFICE CHARLES E. WETHERALD, OE FLINT, MICHIGAN, vAssIGrNoR To GENERAL MOTORS CORPORATION, oF DETROIT, MICHIGAN, A CORPORATION or' DELAWARE METHOD F FQRMING VALVE TAIETS Application led August 7, 1929.' Serial No. 384,067.

This invention relates to valve tappets and more particularly to that type of tappet in which the base or cam-engaging face is formed of one kind of metal, while the stem .5 or shell portion is formed of a different kind of metal.

It has long been recognized that while it is necessary to make the tappet sufficiently large in diameter to provide a proper area of 10 bearing surface between the tappet and the in which the upper portion is in the form of a tubular shell and the cam-engaging face is of some suitable material which will withstand the wear caused by the action of the cams against such face.V

x It has been' found that chilled cast iron or certain alloy steels are ideal materials to be employed in the base of such a tappet, since they possess the proper hardness to withstand the constant impact of the cams. It is not necessary or even desirable that the shell portion be formed of the same material as the base, since'when chilled cast iron is used it would greatly increase the cost to chill the entire outersurface of the tappet,in stead of merely the cam-engaging face. Obviously when alloy .steels'are employed, the cost would be greatly increased .were the entire tappet made of such material. Consequently the practical thing to do is to form the shell of somecheaper material. To cast the shell is not entirely satisfactory since the wall thickness must necessarily be greater and this of course increases the weight which is objectionable. Also, the outside surface of the shell requires considerable machining when cast and if the inside surface is not machined there is a possibility of slightly different weights in/the various tappets, due to molding inaccuracies. If theshell be made in the usual manner from solid steel stock, then a large amount of machining is necessary to remove the material in the center.

5 l It is therefore an obj ectof this invention to motey smooth and quiet performance. F or this reason, an ideal type of tappet is one.

provide a tappetin which the shell portion is .Y formed of solid stock by the extrusion process. In this process a heated billet of metal is placed in a die anda plunger is forced under considerable pressure into the billet, causing the metal in the latter to low axially into the space between the plunger and the die, thusforming a tubular shell. At thevv saine time, part of the metalin thebillet is forced into engagement with a groove formed in a base member of chilled cast iron, alloy steelor some other. suitable material, which has previously been-placed inthe die. The resulting tappet requires no machining other than a slight grinding operation on its eX- terior surface to provide a `proper bearing surface, and all vsuch tappets are necessarily .of exactly the same weight due to the method employed in their manufacture. Such tappets may be produced very rapidly and con- 70 seliently their cost is comparatively low.

' ther -objectsand advantages will be apparent upon referring to the specification and Y accompanying drawings, in which:

Fig. 1 is a fragmentary ,sectional view 75 through the center of the dies employed in the manufacture/of my improved tappet, showing the base and the heated billet in the die beforethe act of extrusion has taken place. l A

Fig. 2 is a view similar to Fig. 1, but showing the lposition of the parts after the act of extrusion.

Fig. 3 is afragmentary vertical section through a portion of an internal combustion '85 engine, showing my improved tappetv assembled therein.

The reference numeral 10 indicatesa stationary die having an aperture 12 therein of the same diameter as that of the tappet to be produced. A movable support 14 fits into the lower end of the aperture -12 and is adapted to be moved up or' down by any suitable means. A plunger 16.01 the same diameter as that of the inside of the' finished tappet 95 is removably mountedin a movable member 18 adapted to be reciprocated by any suitable means which willfurnish suicient pressure to accomplish the act of extrusion to be described later.

The first step in the production of the tappet is to form a base or cam-engaging member 20 of chilled cast iron, alloy steel or other suitable material. An annular groove 22, preferably undercut, is formed in the base. This base is placed in the aperture 12 in such position that the cam engaging face abuts against the support 14, with the groove 22 on the upper side. A billet 24 of any suitable metal, such as ordinary steel, is heated to a temperature sufficiently high to permit the metal to flow when placed under pressure.

This heated billet is just enough smaller in diameter than the diameter of the aperture 12 to permit it to be inserted therein, on top of the base 20.

The plunger 16 is then forced under pressure into the billet, and, since the metal cannot flow radially, it must ow axially downward into the groove 22, and upwardly into the space between the plunger 16 and the die 10. Due to the fact that the metal in the billetl cannot flow radially, there is no possibility of cracks developing in the outer surface of the metal due to expansion. The thickness of the billet is so proportioned that when the plunger has reached the bottom of its stroke,'the metal will have flowed upwardly to such a point as will produce a shell 25 of the desired length. The plunger is then withdrawn, and the tappet is ejected from the die by causing the support 14 to be moved upwardly.

It may not be necessary that the groove 22 be undercut, since when certain combinations Of metals are employed, the upper corner of` the base tends to expand outwardly during the act of extrusion, and thereby serves to lock the base and shell together. In this case an ordinary straight groove in the base is all that need be provided.

After removalfrom the die the outside surface of the shell and the cam-engaging face are ground to provide a smooth surface. In Fig. 3 the tappet is shown assembledin an engine 26. The valve operating push rod 28 or valve stem, as the case may be, ts

into an aperture 30 drilled through the low-A a tappet in which a shell of suitable material is quickly and cheaply formed, and at the in a die, inserting a metal -billet in the die adjacent the base, and then forcing a plunger into said billet to simultaneously cause the metal in the billet to flow into interlocking engagement with said base and to flow into the space between the plunger and the die to form the billet into a tubular shell.

2. The method of forming a valve tappet which consists in placing a cam-engagingl member' having a groove formed therein in a die, inserting a heated metal billet adjacent said member, and then forcing a plunger into said billet to cause the metal in the latter to flow axially into the space betweenthe plunger and the die to form a tubular shell and at the same time to flow axially into the groove to interlock the shell 'with the cam-engaging member.

3. The method of forming a valve tappet which consists in placing a base having a groove formed therein in a die, inserting a heated metal billet in the die adjacent the base, and then forcing a plunger into the billet thereby extruding the metal into the space between the plunger and the die to form a .tubular shell and also into the groove to interlock the base to the shell. 4,.'fThe method of forminga valve tappet which consists in placing a cam-engaging member having an undercut annular groove formed therein in a die, inserting a heated metal billet in said die adjacent said member, and thenl forcing a plunger into said billet to cause the metal in the latter to flow axially into the space between the plunger and the die to form a tubular shell and at the same time to flow axially into the groove to interlock the cam-engaging member with the shell.

In testimony whereof I affix my signature.

CHARLES E. WETHERALD.

same time is interlocked with a base of some I,

material which will provide a proper camengaging face. The resulting tappet is very light in weight and yet provides a large amount of bearing area, thus preventing rapid wear'. Very little machining is necessary and consequently the ta pet may be produced very economically. bviously 

